1. Field
The present disclosure relates to passenger vehicle tires.
2. Description of Related Art
Most passenger vehicle tires comprise:                two beads intended to come into contact with a mounting rim, each bead comprising at least one annular reinforcing structure;        two sidewalls extending the beads radially outwards, the two sidewalls meeting in a crown comprising a crown reinforcement surmounted by a tread;        at least one carcass reinforcement extending from the beads through the sidewalls as far as the crown, the carcass reinforcement comprising a plurality of carcass reinforcing elements and being anchored in the two beads by being wrapped around the annular reinforcing structure so as to form, within each bead, a main portion and a wrapped-around portion;        an apex situated radially on the outside of the annular reinforcing structure and at least partially between the main portion and the wrapped-around portion of the carcass reinforcement, and        an outer strip positioned axially on the outside of the carcass reinforcement and of the apex.        
Recently, there have been proposals to improve the rolling resistance of passenger vehicle tires by optimizing the beads thereof. Document WO 2010/072736 notably teaches the use of special rubber compounds. The outer strip and possibly the apex are made using rubber compounds that have an elastic modulus G′ less than or equal to 15 MPa and a viscous modulus G″ such that:G″[MPa]≦0.2·G′[MPa]−0.2 MPa,the elastic and viscous moduli being measured at 23° C.
That document also recommends further reducing the rolling resistance by optimizing the geometry of that or those portions of the tire that have these moduli: the portion of rubber compound having an elastic modulus G′ less than or equal to 15 MPa and a viscous modulus G″ such that:G″[MPa]≦0.2·G′[MPa]−0.2 MPa,has, in any radial cross section, a thickness E(r), this thickness corresponding to the length of the intersection of the direction perpendicular to the main portion of the carcass reinforcement with the said portion of rubber composition, r denoting the distance separating the intersection of the said direction perpendicular to the main portion of the carcass reinforcement from the radially innermost point of the annular reinforcing structure. The thickness E(r) varies such that, in the range of distances r comprised between 20 and 50 mm, the variation in thickness
      ∂          E      ⁡              (        r        )                  ∂    r  is less than or equal to −0.25 mm/mm (and preferably less than or equal to −0.3 mm/mm) over at least 5 mm. In other words, it is advantageous to ensure that the entity formed by the apex and the outer strip is “squat”, that is to say shorter and wider than in conventional tires.
When implementing this teaching in tires which traditionally have very stiff (in excess of 50 MPa) apexes, it has been found that the incorporation of thick outer strips presents a problem of industrial robustness. Because the quantities of rubber compound involved are fairly great, it is difficult to prevent rubber from moving while the tires are being cured. As a result, the proportion of tires that fail to meet the specifications increases significantly and the movements of the rubber impair the compromise between rolling distance and cornering stiffness.